1. Field of the Invention
The present invention relates generally to a data communication apparatus and method for a CDMA communication system, and in particular, to an apparatus and method for gating data according to whether there is data to transmit.
2. Description of the Related Art
Conventional CDMA (Code Division Multiple Access) mobile communication systems primarily provide voice service. However, future CDMA mobile communication systems will support the IMT-2000 standard, which can provide high-speed data service as well as voice service. More specifically, the IMT-2000 standard can provide high- quality voice service, moving picture service, Internet search service, etc. During data service, IMT-2000 mobile communication systems transmits traffic data over a data channel and transmits control data over a control channel in serial or in parallel with the traffic data. Here, “traffic data” includes voice, picture and packet data, and “control data” includes control and signaling data related to transmission of the traffic data.
In a mobile communication system, data communication is typically characterized by bursts of data transmissions alternating with long periods of non- transmission. The bursts of data are referred to as “packets” or “packages” of data. In the conventional mobile communication system, the base station and the mobile station continuously transmit data on the control channel for a predefined time even when there is no traffic data to transmit. That is, the base station and the mobile station continuously transmit data on the control channel even for the time period where there is no traffic data to transmit, even though this has a deleterious effect on the limited radio resources, base station capacity, power consumption of the mobile station, and interference. This continuous transmission is done in order to minimize the time delay due to sync reacquisition when there is new traffic data to transmit. If there is no data to transmit for a predefined time, the base station and the mobile station release the data channel and the control channel. In this state, if there is new data to transmit, the base station and the mobile station establish new data channel and control channel.
The IMT-2000 mobile communication system standard defines many states according to channel assignment circumstances and state information existence/nonexistence in order to provide packet data service as well as voice service. For example, a state transition diagram for a cell connected state, a radio bearer activated substate (or RBA mode) and a radio bearer suspended substate (or RBS mode) are well defined in 3GPP RAN TS S2 series S2.03, 99.04.
FIG. 1A shows state transition in the cell connected state of the conventional mobile communication system. Referring to FIG. 1A, the cell connected state includes a paging channel (PCH) state, a random access channel (RACH)/downlink shared channel (DSCH) state, a RACH/forward link access channel (FACH) state, and a dedicated channel (DCH)/DCH(Dedicated Channel), DCH/DCH+DSCH, DCH/DSCH+DSCH Ctrl (Control Channel) state.
FIG. 1B shows a radio bearer activated substate (i.e., RBA mode) and a radio bearer suspended substate (i.e., RBS mode) within the DCH/DCH, DCH/DCH+DSCH, DCH/DSCH+DSCH Ctrl state.
In many cases, data transmission is performed intermittently, such as for Internet access and file downloading. Therefore, there occurs a non-transmission period between transmissions of packet data. During this period, the conventional data transmission method releases or continuously maintains the data channel. If the dedicated data channel is released, reconnecting the channel requires a long period of time, making it difficult to provide a corresponding service in real time. On the other hand, if the dedicated data channel is maintained, channel resources are wasted.
The downlink (or forward link), which transmits signals from the base station to the mobile station, includes the following physical channels. Physical channels which depart from the scope of the invention will not be described for the sake of simplicity. The downlink physical channels involved in the invention include a dedicated physical control channel (hereinafter, referred to as DPCCH) in which pilot symbols are included for sync acquisition and channel estimation, a dedicated physical data channel (hereinafter, referred to as DPDCH) for exchanging traffic data with a specific mobile station, and a down link shared channel(DSCH) for transmitting traffic data to multiple mobile stations. The downlink DPDCH includes the traffic data, and the downlink DPCCH includes, at each slot, the control data such as transport format combination indicator (hereinafter, referred to as TFCI), transmit power control (hereinafter, referred to as TPC) information and pilot symbols, which are time multiplexed within one slot. The uplink (or reverse link), which transmits signals from the mobile station to the base station, also has an uplink dedicated control channel and dedicated data channel.
Embodiments of the present invention will be described with reference to the case where the frame length is 10 msec and each frame includes 16 slots, i.e., each slot has a length of 0.625 msec. Alternatively, embodiments of the present invention will also be described with reference to another case where the frame length is 10 msec and each frame includes 15 slots, i.e., each slot has a length of 0.667 msec. The slot may have either the same length as a power control group (PCG) or a different length from the power control group. It will be assumed herein that the power control group (0.625 msec or 0.667 msec) has the same time period as the slot (0.625 msec or 0.667 msec). The slot includes pilot symbol, traffic data, transport format combination indicator, and power control command bit. The values stated above are given by way of example only.
FIG. 2A shows a slot structure including the downlink DPDCH and DPCCH. In FIG. 2A, although the DPDCH is divided into traffic data 1 (Data1) and traffic data 2 (Data2), there is a case where traffic data 1 does not exist and only traffic data 2 exists according to the types of the traffic data. In FIG. 2A, the DPCCH is constructed in the order of TFCI, TPC, and PILOT. Table 1 below shows the symbols constituting the downlink DPDCH/DPCCH fields, wherein the number of TFCI, TPC and pilot bits in each slot can vary according to a data rate and a spreading factor (SF).
Unlike the downlink DPDCH and DPCCH, uplink DPDCH and DPCCH for transmitting signals from the mobile station to the base station are separated by independent channel separation codes.
FIG. 2B shows a slot structure including the uplink DPDCH and DPCCH, wherein reference numeral 211 indicates a slot structure of the DPDCH and reference numeral 213 indicates a slot structure of the DPCCH. In FIG. 2B, with regard to the DPCCH, the number of TFCI, TPC and pilot bits can vary according to the service option (including the type of the traffic data and the transmit antenna diversity) or a handover circumstance. Tables 2 and 3 below show the symbols constituting the uplink DPDCH and DPCCH fields, respectively.
TABLE 1Downlink DPDCH/DPCCH FieldsChannelChannelSymbolDPDCHDPCCHBit RateRateBits/FrameBits/SlotBits/Slot(kbps)(ksps)SFDPDCHDPCCHTOTBits/SlotNdata1Ndata2NTFCINTPCNpilot16851264961601022024168512321281601002224321625616016032020280283216256128192320200822864321284801606404062402864321284481926404042422812864641120160128080145602812864649922881280806568282561283224001602560160301200282561283222722882560160221208285122561648322885120320622400216512256164704416512032054240821610245128995228810240640126496021610245128982441610240640118496821620481024420192288204801280254100802162048102442006441620480128024610088216
TABLE 2Uplink DPDCH FieldsChannelBit RateChannel Symbol(kbps)Rate (ksps)SFBits/FrameBits/SlotNdata1616256160101032321283202020646464640404012812832128080802562561625601601605125128512032032010241024410240640640
TABLE 3Uplink DPCCH FieldsChannelChannel BitSymbolRate (kbps)Rate (ksps)SFBits/FrameBits/SlotNpilotNTPCNTFCINFBI161625616010622016162561601082001616256160105221161625616010720116162561601062021616256160105122
Tables 1 to 3 show an example where there exists one DPDCH which is a traffic channel. However, there may exist second, third and fourth DPDCHs according to the service types. Further, the downlink and uplink both may include several DPDCHs. Although the base station transmitter and the mobile station transmitter will be described with reference to the case where there exist three DPDCHs, the number of DPDCHs is not limited.
FIG. 3A shows a structure of the conventional base station transmitter. Referring to FIG. 3A, multipliers 111, 121, 131 and 132 multiply outputs of DPCCH, DPDCH1 (or DSCH), DPDCH2 and DPDCH3 data generators 101, 102, 103 and 104, which have undergone channel encoding and interleaving, by their associated gain coefficients G1, G2, G3 and G4, respectively. The gain coefficients G1, G2, G3 and G4 may have different values according to circumstances such as the service option and the handover. A multiplexer (MUX) 112 time-multiplexes the DPCCH signal and the DPDCH1 signal into the slot structure of FIG. 2A. A first serial-to-parallel (S/P) converter 113 distributes the output of the multiplexer 112 to an I channel and a Q channel. Second and third S/P converters 133 and 134 S/P-convert the DPDCH2 and DPDCH3 signals and distribute them to the I channel and the Q channel, respectively.
The S/P-converted I and Q channel signals are multiplied by channelization codes CCh1, CCh2 and CCh3 in multipliers 114, 122, 135, 136, 137 and 138, for spreading and channel separation. Orthogonal codes are used for the channelization codes. The I and Q channel signals multiplied by the channelization codes in the multipliers 114, 122, 135, 136, 137 and 138 are summed by first and second summers 115 and 123, respectively. That is, the I channel signals are summed by the first summer 115, and the Q channel signals are summed by the second summer 123. The output of the second summer 123 is phase shifted by 90° by a phase shifter 124. A summer 116 sums an output of the first summer 115 and an output of the phase shifter 124 to generate a complex signal I+jQ. A multiplier 117 scrambles the complex signal with a PN sequence Cscramb which is uniquely assigned to each base station, and a signal separator 118 separates the scrambled signal into a real part and an imaginary part and distributes them to the I channel and the Q channel. The I and Q channel outputs of the signal separator 118 are filtered by lowpass filters 119 and 125, respectively, to generate bandwidth-limited signals. The output signals of the filters 119 and 125 are multiplied by carriers cos {2πfct} and sin {2πfct} in multipliers 120 and 126, respectively, to frequency-up convert the signals to a radio frequency (RF) band. An adder 127 sums the frequency-shifted I and Q channel signals.
FIG. 3B shows a structure of the conventional mobile station transmitter. Referring to FIG. 3B, multipliers 211, 221, 223 and 225 multiply outputs of DPCCH, DPDCH1, DPDCH2 and DPDCH3 data generators 201, 202, 203 and 204, which have undergone channel encoding and interleaving, by their associated channelization codes Cch1, Cch2, Cch3 and Cch4, respectively, for spreading and channel separation. Orthogonal codes are used for the channelization codes. The output signals of the multipliers 211, 221, 223 and 225 are multiplied by their associated gain coefficients G1, G2, G3 and G4 in multipliers 212, 222, 224 and 226, respectively. The gain coefficients G1, G2, G3 and G4 may have different values.
The outputs of the multipliers 212 and 222 are summed by a first summer 213 and output as an I channel signal, and the outputs of the multipliers 224 and 226 are summed by a second summer 227 and output as a Q channel signal. The Q channel signal output from the second summer 227 is phase shifted by 90° in a phase shifter 228. A summer 214 sums the output of the first summer 213 and the output of the phase shifter 228 to generate a complex signal I+jQ. A multiplier 215 scrambles the complex signal with a PN sequence Cscramb which is uniquely assigned to the mobile station, and a signal separator 229 separates the scrambled signal into a real part and an imaginary part and distributes them to the I channel and the Q channel. The I and Q channel outputs of the signal separator 229 are filtered by lowpass filters 216 and 230, respectively, to generate bandwidth-limited signals. The output signals of the filters 216 and 230 are multiplied by carriers cos {2πfct} and sin {2πfct} in multipliers 217 and 231, respectively, to frequency- up convert the signals to a radio frequency (RF) band. An adder 218 sums the frequency- up-converted I and Q channel signals.
FIG. 4A shows a conventional method of transmitting the downlink DPCCH and the uplink DPCCH in the RBS mode when transmission of the uplink DPDCH is discontinued. FIG. 4B shows a conventional method of transmitting the downlink DPCCH and the uplink DPCCH in the RBS mode when transmission of the downlink DPDCH is discontinued.
As illustrated in FIGS. 4A and 4B, the mobile station constantly transmits the uplink DPCCH in the RBS mode in order to avoid a resynchronization acquisition process in the base station. When there is no traffic data to transmit for a long time in the RBS mode, the base station and the mobile station make a transition to an RRC (Radio Resource Control) connection released state. In this state, transmission of the uplink DPDCH is discontinued, but the mobile station transmits pilot symbols and TPC (Transmit Power Control) bits over the DPCCH until the transition is completed, thereby there is an unnecessary interference in the uplink. The interference of the uplink causes a decrease in the capacity of the uplink.
In the conventional method, although continuous transmission of the uplink DPCCH is advantageous in that it is possible to avoid the sync reacquisition process in the base station, it increases interference to the uplink, causing a decrease in the capacity of the uplink. Further, in the downlink, continuous transmission of the uplink transmission power control (TPC) bits causes an interference of the downlink and a decrease in the capacity of the downlink. Therefore, it is necessary to minimize the time required for the sync reacquisition process in the base station, to minimize the interference due to transmission of the uplink DPCCH signal and to minimize the interference due to transmission of the uplink transmission power control(TPC) bits over the downlink.